The Role of Heterogeneous Chemistry in Ozone Depletion and Recovery

Anthropogenic chlorine from over half a century of CFC emissions is the main contributor to global stratospheric ozone depletion. Stratospheric chlorine gets converted from reservoir species into reactive ones capable of catalytic ozone destruction via heterogeneous chemical reactions on various surfaces. Identification of stratospheric ozone changes attributable to ozone depleting substances and actions taken under the Montreal Protocol requires evaluation of confounding influences from volcanic eruptions due to the enhanced depletion caused by the greater surface areas available for heterogeneous reactions on volcanic sulfuric acid aerosols. A suite of recent simulations with the WACCM chemistry-climate model from 1979-2014 show that increased stratospheric aerosol loading from volcanic eruptions after 2004 impeded the rate of ozone recovery from 1999 to 2014. In contrast, eruptions increased ozone loss rates over the depletion era from 1980 to 1998. These findings reinforce the need for accurate information regarding stratospheric aerosol loading when modeling ozone changes, particularly for the challenging task of accurately identifying the early signs of ozone healing distinct from other sources of variability.

Anthropogenic chlorine from over half a century of CFC emissions is the main contributor to global stratospheric ozone depletion. Stratospheric chlorine gets converted from reservoir species into reactive ones capable of catalytic ozone destruction via heterogeneous chemical reactions on various surfaces. Identification of stratospheric ozone changes attributable to ozone depleting substances and actions taken under the Montreal Protocol requires evaluation of confounding influences from volcanic eruptions due to the enhanced depletion caused by the greater surface areas available for heterogeneous reactions on volcanic sulfuric acid aerosols. A suite of recent simulations with the WACCM chemistry-climate model from 1979-2014 show that increased stratospheric aerosol loading from volcanic eruptions after 2004 impeded the rate of ozone recovery from 1999 to 2014. In contrast, eruptions increased ozone loss rates over the depletion era from 1980 to 1998. These findings reinforce the need for accurate information regarding stratospheric aerosol loading when modeling ozone changes, particularly for the challenging task of accurately identifying the early signs of ozone healing distinct from other sources of variability.